Mineral Planets

Let's use the term mineral planet for planets that an alien species could turn into a sustainable habitat. These are a far cry from an origin planet, which is one which could give birth to life by evolving its own first cells. It is a far cry from a seedable planet, which is one which could not evolve its own starting cells, but which could take a seed of some sort of cells and have them multiply and eventually evolve into something interesting, like an alien civilization. Instead, a mineral planet is one where an advanced civilization could establish mines and habitats, on the surface or below it, and thereby produce enough resources, energy and minerals, to sustain an alien colony without any continuing support from the home planet. It has to persist for a long period. 

There may be very few origin planets in the galaxy, and somewhat more seedable planets, and maybe a huge number of mineral planets. One implication of such a lopsided ratio would be that mineral planets can be stepping stones for an alien civilization to cross the galaxy. Note that some or all alien civilizations may adopt the goal of seeding as many seedable planets as they can, following a philosophy that life is its own goal, and that just like planet-bound species try to disperse as much as they can, alien civilizations try to spread life as much as they can. Traveling 300 light years from a civilization's origin planet to the nearest seedable planet might be simply too much to do, and so finding a network of mineral planets in the general direction of that seedable planet would allow them to gradually work their way over to it, and when close enough, to accomplish the seeding effort with more payload and duration in orbit that they could have if they had to travel 300 light years.

Reliability might play a role here. If a speed of 1% of the speed of light is used as a guess of the maximum speed the civilization might attain with its colony ships, this means 1000 years of reliability is necessary to go to the nearest mineral planet, but 30000 years would be necessary for the closest seedable planet. If the probability of enough equipment lasting 1000 years can get raised to 98%, a risk the civilization might be willing to take, the same equipment has a probability of the same quorum still working after 30000 years of travel of only 55%.

Monitoring a seedable planet is also easier from 10 light years away than 300. It might be that seeding a planet is necessarily a very chancy situation, and multiple visits are the only way to accomplish it and verify that it has been accomplished in such a way that a billion years of evolution or two can follow without total extinction. Maybe seeding can only be handled by landing a small colony on the planet, and staying there for a long period. This could also be accommodated better from a nearby solar system than from a distant one.

Is there anything which can be credibly said about the prevalence of mineral planets? The formation of stars seems to leave a disk of matter revolving around it, which can turn into planets. This is a matter of the disposition of angular momentum, and how hard it is to collect it all in a central body. Everywhere we look we see planets, and our ability to find them is not so great right now, so there are probably many more per cubic light year than we have discovered in our locality. If there are several planets on the average per star, how likely is it that at least one of them is a mineral planet?

To be a mineral planet, the planet has to be mineable and habitable. Planets too close to the star are too hot on the surface to establish a colony, and the temperature below the surface would be higher than the average temperature at any latitude. The orientation of the planet would indicate the spread of temperatures over the planet, from pole to equator, and indicate if there was any latitude above which a colony ship could land and stay without thermal damage. Phase-locked planets provide a different criteria, but if the north pole of a non-rotating planet is designated as the closest-to-star point, then again, there may a latitude beyond which the ship could land.

Too much atmosphere would interfere with colonization, and planets might be excluded on this basis. Since smaller planets cannot long hold onto the atmospheres they have at formation, size is an indicator of this problem. The maximum size depends on the distance from the star, as it is easier to hold onto an atmosphere if the planet is far from the star and the atmosphere is very cold. Cold gases evaporate much more slowly.

Another question to be asked is the radiation level. If the star is a very active one, the colony ship would not even be able to come in close to it, unless some sort of shielding was build into the hull. Perhaps advanced engineering could figure out a way to get a mine dug, and alien colonists down into the mine without receiving too much radiation. Once under the surface, all the radiation is absorbed before reaching them. This is an interesting project to be considered.

With all these factors eliminating candidates, how much might be left? Our surveys of exo-planets are too limiting to calculate this number, but it might be that 90% are no good, meaning one in three stars, of middle class, has a candidate. There is more to being a mineral planet that simply being mineable with a surface not too lethal. There has to be the right mix of minerals.

An alien body has certain needs for elements, and alien technology has a different set of requirements for elements. Together they comprise the shopping list of elements, or rather minerals from which the needed minerals can be extracted. Some small molecules might also be extracted, principally water and carbon dioxide, maybe some others. The distribution of elements on a planet is a result of the original composition of the gas cloud, which comes from the effect of nearby supernovas in the cloud's history. Then there is the condensation question and the diffusion question, with minerals forming as elements and condensing into dust, and then being filtered by the solar wind and light output from the star over millions of years. After that, when the planet forms, geology plays a role in determining which minerals are at the surface.

The only planet we have any experience with is Earth, and it can provide us with a model problem. Suppose there was a planet in a state just like modern Earth but without any atmosphere, without any fossil fuels, no life, and of course no people, meaning no mining. Could an alien colony ship find the right minerals, in accessible form, so that it could produce a sustainable colony here? Perhaps U-235 is the key. We can mine uranium ore, refine it, enrich it, build a reactor, and extract more energy than was needed to construct the reactor and keep it fueled. Alien reactors should be even more efficient in the use of fissionable and fertile fuel than ours are, as we have had only a few decades of experience with fission power. Perhaps the guess of one solar system in three having a mineral planet is not too far from the truth. 

Choosing Colony Planets

An alien civilization with a philosophy of life requiring it to spread and disperse life throughout the galaxy, as far as it can, would need to be very circumspect about where to send a seedship. This adventure would require a great amount of effort from the civilization, and perhaps a good fraction of the resources available to it. On Earth, we have not even begun to figure out how this might be done, but we can assure ourselves this is not going to be easy for any civilization. As little would be left to chance as possible.

If we ask ourselves about the possibility of our civilization encountering another one, knowing where they would likely be is a critical question. They start on their origin planet, but then where do they go? We have learned over the last decade or two that there are huge numbers of exo-planets in the galaxy, but of these, which ones might be even initial candidates for an alien civilization's colonies? What are the characteristics of a possible colony planet? If we know that, then we can concentrate our search for alien life, or rather alien civilization, on that class of planet, and spend less on others.

What we cannot assume is that they will only go to other planets which have already originated life. If their philosophy and reason for continuing their existence is to spread life throughout the galaxy, an origin planet would be low on their list – it already has life and there is no need to go there and seed it. That would be superfluous. Instead, they would want to go where there is no life and is not likely to be if the planet is left to itself. Not just any planet would do. There are certainly some detailed criteria for a reasonably nearby planet, within a hundred or two light years, to even be considered as a possibility.

Many planets might only support the alien civilization itself, and not some ecology of plants, animals, microbes or whatever on it.  Their mandate is to spread life, but if the only way that can be done is to establish a colony, then that is the solution to the lack of planets which might be harbors for primitive life.  The alien civilization can set up colonies in many places, but needs to discriminate as to what distinguishes one possibility from another, as far as spreading life goes.  

One dominant aspect of the choice is sustainability. Sustainability means, for some particular alien species or collection of them, the ability to live for a very long period, measured in lifetimes, on the resources and energy located near and accessible to them. It includes the idea that the population should be able to grow up to some minimum value and still live there for that long period. It is about resources existing on the planet, near the surface, but also about being able to extract enough materials to make an energy source that produces much more energy than all the energy needed to collect and process the materials used in the energy generation and distribution process. There must be enough surplus energy for the other half of the problem, providing all the components, such as habitat and food, needed to sustain the new alien population.

The colony starts out with only the equipment that can be carried on the seedship. The development of the colony would consist of several preliminary stages before the uniform growth stage expands the colony up to the desired population. The first stage involves the landing of whatever is necessary to initiate power production with a minimally sized power reactor, create a habitat, and locate and start to mine and process all necessary mineral deposits. A central manufacturing complex would need to be created that can produce, from the ores found, all the specialized items needed for all the operations of the civilization.

Control of this process is not so critical. Can this be done in an automated fashion, or is it necessary to spend time in orbit, gestating the first generation of aliens, before sending them down with the initial lander? Whether the seeding operation is under AI control or under alien control, much the same steps have to be done. The principal difference is that habitats need to be made for the alien landing party, or some additional manufacturing facilities need to be made to enable expansion of the AI capability.

The question of sustainability is not easy to calculate in advance. Yet this is what an alien civilization must do before attempting to spread its population to a new planet or satellite in a distant solar system. They must make an estimate of whether or not a colony could survive on an exoplanet before taking the extreme expense of sending a seedship there The question is not just can the colony survive for a while, but survive and build a large civilization on the planet. The ultimate question involves the possibility that an alien colony, on a colony planet, could create a civilization large enough to send out its own seedship. If the colony planet was a dead-end, without enough resources for the civilization to grow large enough for the project of going out yet further to another colony planet, it should not be chosen.

The calculation depends on what goes along with the seedship. How much energy does it carry to support the transition from nothingness on the planet to a viable colony? Before this is used up, a seedship must arrange for native energy sources on the planet. This might seem to mean a uranium mine, but the uranium metal is actually a small part of what is needed to build an energy-producing fission reactor. Some parts for the first reactor might come from the ship, and this means that sustainability in energy is going to be developed in stages. The energy from the first reactor would need to be deployed toward a variety of tasks.

Total sustainability means that all mandatory mineral resources are present in the planet's crust, easily accessible, and with not too large a cost in transporting them from their mining site to the central location where the colony's initial population will be centered. For an alien civilization attempting to create a very credible and accurate estimate of this, which they would need before a launch, they would have to first collect all possible information about the planet and the solar system it is located in. The only way to do this from their planet is to build huge telescopes, and it also means asymptotic technology as far as planet formation goes, i.e. having geology completely understood, from the time of the gas cloud through all the changes that go on with the crust of the planet. They would need to be able to tell from the spectrum of the star what the gas cloud that created it contained, as for different elements and the relative concentrations of each.

At this point in Earth science, we have not attempted to make any such calculations, and so we don't really know if it is possible, or how accurate it might be. The accuracy is likely a function of the age of the star, as mixing will take place over its history, and the origination elements will also be burned up as they go deeper into the star's core. Light comes from the star's corona, where elements will linger the longest and where transmutation would be slowest.

Data is also available from the spectrum of the planet itself, where it is simply the reflected spectrum of the parent star. This might tell what was in the atmosphere, and what the large areas of the surface have, to a degree. Reflection spectroscopy is necessarily more difficult that emission spectroscopy, but if the telescope is large enough to portray the planet across many pixels, then some information might be gained from each one. Planets rotate, but that should not interfere with the data collection, once the images start coming in. A telescope of large size, perhaps ten kilometers or more in aperature, would be needed.

Information about the nature of the gas cloud that formed the target exo-planet might be gained also by looking at the other planets of the solar system containing it. A gas cloud which undergoes the great transformation from a rotating self-gravitating glob of dust and gas into a proto-star and spinning disk would also have undergone much diffusion, and this implies that at the radius where the target exo-planet condenses there would be some distribution of elements, but at the radii where other planets condense, there would be a different one, and knowing each of them helps the alien scientists to determine the larger picture of the composition and evolution of the cloud.

One kink in this process is that planets don't necessarily stay at the radius where they condense. The effect of the largest planet or the largest few planets might, in some instances, drive a smaller planet to a different orbital radius. The largest planets might also mutually share angular momentum, and drift to different radii as well. Can this be determined from telescopic observations so that the data from all of the planets can be put to use? A good question, and one we on Earth have not begun to fathom.

None of the scientific steps needed seem to be impossible, even from the viewpoint we have now, with our very limited science. An alien civilization a few hundred years further in science than ours should be able to accomplish them, as far as it is possible. Once this mass of data has been collected, perhaps over a century of observation, the estimation of which visible planet would be best to seed can be done.

Hunting for Life in the Milky Way

In earlier posts, there was some discussion of what would be the goals of an advanced alien civilization, assuming they had come together to choose one and then to work on it. In a different blog, some more thinking on this matter indicated that the most reasonable and likely goal of the civilization is that of life itself, which is best broken down into five separate goals, survival, reproduction, adaptation, evolution and dispersion. These goals imply many choices that the alien civilization would make, in order to further their alignment with these life goals. The last goal is dispersion, and that means first expansion all over the planet, then the solar system, and then outwards into the galaxy. Just think for a minute what this implies: all or most advanced alien civilizations are going to attempt colonization and seeding, both of which support the dispersion of life.

Neither of these tasks are easy, as has been noted in all the posts in this blog on these topics. Colonization means setting up some replica of the alien civilization on an exoplanet ,while seeding means starting out life with the alien version of DNA on some planet which doesn’t have the prerequisites to become an origin planet on its own, but can support life, being in the habitable zone plus all the other conditions. Current theory here on Earth indicate the cells that did that were cyanobacteria.

Looking for seeded planets would likely be the same as looking for origin planets. Seeding might put photosynthetic organisms into a planetary ocean, and then, after a few hundreds of millions of years, an oxygen atmosphere might exist, which is a tremendous benefit for evolution, allowing life to expand beyond chemotrophs and cyanobacteria cells to a food chain. The oxygen in a seeded planet’s atmosphere would look the same as in an origin planet’s atmosphere.

So, assuming most of the alien civilizations do both seeding of potential life-supporting planets and colonization of others, which are not able to support life, but which provide the resources necessary for the alien civilization to sustain itself for a long time. Which ones should be looked for?

Seeding a planet gets over the hump of life origination, which might be tremendously difficult, rare and improbable, at least according to one theory, mine. Is evolution fairly certain after that, or are there more highly improbable-to-overcome barriers along the way to intelligence? Suppose there aren’t. Suppose evolution is as easy as rolling down a hill. However, it takes a long time. Earth is our only example here, and life took about two and a half billion years after the atmosphere changed to partially oxygen to evolve to intelligence. This means that any alien civilization which evolved in the last two to three billion years has not had enough time yet for their first example of seeding to have led to a new alien civilization, evolved from cyanobacteria to tool-using creatures of one form or another.

This raises the obvious question of when, in the history of the galaxy, was life likely to originate? There are stars around which are ten or so billion years old. Could these have had planets soon after they formed, and perhaps one which met the prerequisites for life to originate? Unfortunately, current astronomical tools do not allow us to figure out much of the history of the galaxy. It likely started out as a gas blob, and condensed irregularly, with stars forming all over it, but more in the denser region in the center. Gas was more dense that now, as by now much has been consumed in star formation, and that implies that stars which formed early would be larger. Large stars live short lives, and end in a supernova explosion. There would not have been the neat division of the galaxy into the disk and the central bulge, so star motion would have been more random and Boltzmann-like. Neither of these two things bode well for planets. Supernovas going off near a planetary system sterilize it, but may also disturb planetary orbits, causing them to be ejected or rarely crash into the star. The passage of a nearby star does the same thing, pulling planets out of their orbit, leading to a planet-planet interaction where the smaller ones get ejected. So, while little definitive is known, it would seem likely that planetary formation in a system which perseveres long enough to originate and evolve life is more likely in the later stages of the galaxy and out in the disk. Finding planets to seed would also be more likely in these conditions.

Putting this together means that seeded planets might be around, but life on them is too young to have evolved into an advanced civilization. There really is a double time here. For life to originate and produce an alien civilization, capable of star travel, might take four billion years since the planet formed into a habitable world, with the right temperatures and everything else needed for life. Then if that civilization seeds another planet, we have another three billion years or so to wait. That is seven total, and seven billion years ago, there might have been so much turmoil in the galaxy that life couldn’t originate and evolve. So, planets which have been seeded might be common, and even many which have had the few hundred million years to produce an oxygen atmosphere. But if we are hunting for alien civilizations, seeded planets are not worth the effort. That leaves origin planets and colonized planets.

The previous post, on frozen worlds, indicates that colonized worlds, if the aliens choose worlds which are the easiest to colonize and which will sustain them for a long time, might look absolutely different from origin worlds. It also indicated, because of the very different time scales involved, that there could be very many of them all over the Milky Way, or at least out in the disk. The idea was simple: if there are sufficient resources on the planet, fusible and fissionable elements, plus all the other minerals necessary to supply the civilization with its raw materials, buried in the ground, they can simply build their civilization under the surface, on a frozen world and maybe some not so frozen. The ratio between colonized worlds and origin worlds might be a thousand to one. There would also be much larger numbers of previously colonized worlds where the alien civilization has used up the minerals and life on the planet was no longer sustainable for them.

How do you detect a mine shaft and a starship landing zone? Maybe there would have to be some surface transportation, if they needed to have mines in multiple locations. It might be possible, with a kilometer sized telescope, to see large oceans on an exoplanet in our vicinity, but even one ten times larger than that could not detect something as small as tens of meters or even a kilometer in size. Looking for a tiny heat source is conceivable, but unlikely as the resolution at deep infrared wavelengths is so much less than in the visible. If the concepts trotted out here and in the last post are viable, it means that alien civilizations are not detectable, and they would have no interest in coming to Earth, either for seeding as we are way past that, or colonizing as there are too many potential difficulties. It wouldn’t align with their goal of dispersing life at all to visit Earth. So the only thing we have any hope of doing is detecting an origin world, but if there is only a few of them,they might be on the other side of the Milky Way or in a different spiral arm. Perhaps a double hope of there being easy ways to originate life and our detecting oxygen in exo-planet atmospheres is the only possible salvation for the quest to find aliens.